STM/AFM study of Ge quantum dots grown on Si(111)

We study by Scanning Tunneling Microscopy (STM) and Atomic Force Microscopy (AFM) in situ the evolution of Ge islands grown by Physical Vapor Deposition (PVD) on 7x7 Si(111) reconstructed surfaces. On the 5x5 reconstructed Wetting Layer large 3D islands form whose average lateral dimension is about 200 - 500 nm. The statistical distribution of the island shapes has been analyzed, showing that three types of shapes coexist under certain conditions: strained, relaxed and ripened (atoll-like) islands. By Scanning Probe Microscopy (SPM) it was possible to measure the contact angles of the island facets and to observe the depletion of the substrate around the ripened islands. All these features are attributed to the misfit strain. These findings successfully compare with a recent theoretical model.